Found no official dimensions, but I know I read about the dimensions of the spacers somewhere on the forums, so I though this are the correct ones. When I assemble the wheels it looks like this: https://imgur.com/a/8aY8jIx

It doesn’t matter that much as long as the wheel doesn’t easily move on the bearings. They make spacers specifically for skate wheels, there are a few different sizes. The ones I carry are 10mm and fit both inline and skateboard wheels.